1. Field of the Invention
This invention relates to a wire electrode type electric discharge machining device, and more particularly relates to the structure of the device which prevents the application of as external force to its lower arm for supporting a wire guide.
2. Description of the Prior Art
The conventional wire electrode type electric discharge machining device has been introduced by Japanese Patent Application Unexamined Publication No. 89524/82 and Japanese Utility Model Application Publication No. 30031/82, etc.
FIG. 1 is a perspective view showing an example of the arrangement of a conventional wire electrode type electric discharge machining device.
In FIG. 1, a wire electrode 10 is guided by an upper wire guide 12 and a lower wire guide 14 which are located bove and below a workpiece 16, respectively, so that the wire electrode 10 is slidable in the up-and-down directions. A surface plate 18 is placed on a machining tank 20 to hold the workpiece 16. An upper arm 22 is located above the workpiece 16 serves to hold the upper wire guide 12, the upper arm 22 being secured to a column 24 of the machine body. A lower arm 26 is located below the workpiece 16 serves to hold the lower wire guide 14 in such a manner that the lower wire guide 14 confronts the upper wire guide 12 held by the upper arm 22. A splash preventing body 28 is so arranged as to prevent machining solution (generally water) jetting from the respective upper and lower wire guides 12 and 14 towards the workpiece 16 from splashing. The splash preventing body 28 is made up of a frame 32, a seal 30 which is provided inside the frame 32 as to being slidable in the longitudinal direction of the lower arm 26, a pair of pleated members 34 connected to both sides (laterally of the lower arm 26) of the frame 32 in such a manner that they are expandable and contractable, and a support 35 which fixes both ends of the pleated members 34 to the machining tank 20. FIG. 2 is a sectional view of the body of the electric discharge machining device thus constructed.
The operation of the electric discharge machining device thus constructed will be described.
In machining the workpiece 16, the wire electrode 10 is fed downwardly or upwardly with a wire feeding system (not shown).
The workpiece 16 can be moved relative to the wire electrode 10 in the horizontal direction by means of an X-Y cross table (not shown) with the aid of the machining tank 20 and the surface plate 18. In machining the workpiece 16, the X-Y cross table (not shown) is moved so that the workpiece 16 confronts the wire electrode 10 with a small space therebetween, and the machining solution is jetted from the upper and lower wire guides 12 and 14 into the space. Under this condition, explosive electric discharge is caused between the wire electrode 10 and the workpiece 16 through the machining solution. As a result, the wire electrode and the workpiece 16 are partly blown away. In this operation, wherein the wire electrode 10 is being fed continuously, the wire electrode 10 is not cut off. The workpiece can be machined as required by moving the X-Y table.
The machining solution jetting during the machining operation may flow down the lower arm 26; however, it is blocked by the seal 30, so that it is recovered into the machining tank 20 without flowing over the splash preventing body 28.
The conventional wire electrode type electric discharge machining device is constructed as described above. Therefore, in the case where the table is moved laterally of the lower arm 26 to machine the workpiece, an external force produced with expansion and contraction of the pleated members 34 acts on the lower arm 26, so that the lower arm 26 is deformed as shown in FIG. 3; that is, the lower wire guide 14 held by the lower arm 26 is shifted by eX in the X-direction and eY in the Y-direction from the upper wire guide 12. Because of this shift, the workpiece machined is not correct in configuration; that is, the workpiece cannot be machined with high accuracy. Furthermore, other external forces, which are produced for instance when scraps cut off the workpiece are brought into contact with the lower arm 26, act on the lower arm 26, thus lowering the maching accuracy greatly.